From: Dmitriy Vyukov <dvyukov@google.com>
Date: Thu, 7 Mar 2013 17:39:59 +0000 (+0400)
Subject: runtime: fix deadlock
X-Git-Tag: go1.1rc2~647
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=cb945ba6ba23772336bf02fd2364c3df9e9233e0;p=gostls13.git

runtime: fix deadlock
The deadlock episodically occurs on misc/cgo/test/TestCthread.
The problem is that starttheworld() leaves some P's with local work
without M's. Then all active M's enter into syscalls, but reject to
wake another M's due to the following check (both in entersyscallblock() and in retake()):
if(p->runqhead == p->runqtail &&
        runtime·atomicload(&runtime·sched.nmspinning) +
        runtime·atomicload(&runtime·sched.npidle) > 0)
        continue;

R=rsc
CC=golang-dev
https://golang.org/cl/7424054
---

diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index 4ce0a718cd..d0f6745aa7 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -392,7 +392,7 @@ mhelpgc(void)
 void
 runtime·starttheworld(void)
 {
-	P *p;
+	P *p, *p1;
 	M *mp;
 	bool add;
 
@@ -405,6 +405,7 @@ runtime·starttheworld(void)
 		procresize(runtime·gomaxprocs);
 	runtime·gcwaiting = 0;
 
+	p1 = nil;
 	while(p = pidleget()) {
 		// procresize() puts p's with work at the beginning of the list.
 		// Once we reach a p without a run queue, the rest don't have one either.
@@ -414,8 +415,9 @@ runtime·starttheworld(void)
 		}
 		mp = mget();
 		if(mp == nil) {
-			pidleput(p);
-			break;
+			p->link = p1;
+			p1 = p;
+			continue;
 		}
 		if(mp->nextp)
 			runtime·throw("starttheworld: inconsistent mp->nextp");
@@ -428,6 +430,13 @@ runtime·starttheworld(void)
 	}
 	runtime·unlock(&runtime·sched);
 
+	while(p1) {
+		p = p1;
+		p1 = p1->link;
+		add = false;
+		newm(nil, p);
+	}
+
 	if(add) {
 		// If GC could have used another helper proc, start one now,
 		// in the hope that it will be available next time.